So aside from ST-E3 and 600EX-RT (with radio and line-of sight wireless) there are now 3 options for light-pulse line-of-sight wireless mastering available from Canon. Each with it's own set of advantages and disadvantages:

Unfortunately neither one of the "small, light & cheap" options has all desired functionality.

And regrettably none of Canon's wireless mastering options offers 2nd curtain sync whereas all of Nikons's wireless CLS options do provide 1st, 2nd curtain and HSS in wireless mode - but they got no radio wireless as of yet. ;-)

And regrettably none of Canon's wireless mastering options offers 2nd curtain sync whereas all of Nikons's wireless CLS options do provide 1st, 2nd curtain and HSS in wireless mode - but they got no radio wireless as of yet. ;-)

I'm still amazed why Canon didn't add 2nd curtain wireless at least to the new 600rt protocol - since rt is not backward compatible anyway, it would have been easy to add this feature as ettl-iii. But maybe it'll be on the 660rt :-p ?

And regrettably none of Canon's wireless mastering options offers 2nd curtain sync whereas all of Nikons's wireless CLS options do provide 1st, 2nd curtain and HSS in wireless mode - but they got no radio wireless as of yet. ;-)

I'll have to check again but I was fairly sure second curtain sync was able to be enabled in the camera menu when i had the 90 ex on it, the tiny size and weight are definately a good plus for this little guy

I'll have to check again but I was fairly sure second curtain sync was able to be enabled in the camera menu when i had the 90 ex on it, the tiny size and weight are definately a good plus for this little guy

@wickidwombat: could you please take a look into this feature, once your time allows? I am fairly certain 2nd curtain Sync will not be available in wireless mode. However, I would be more than happy if I were proven wrong on this one and would immediately order a 90EX. :-) Thanks!

A couple of observations from using the 7D. The on-camera flash must fire for the trigger to work. (The flash has no effect on the exposure as it is synced to fire before the shutter opens, but it must fire.) This has a tendency to overheat the flash very quickly. Once it overheats, it shuts down until it cools off. The net result is that you are out of business until it cools down. Embarrassing and frustrating if you are in the middle of shooting a portrait.

I don't know if the small 90EX fires when you use it to trigger a slave or if it is subject to the same overheating, but I wouldn't be surprised if it does overheat quickly, given its small size. Just something to be cautious about.

After several embarrassing and frustrating incidents, where the flash quit triggering my 580 II's, I decided to go for the Yongnuo knockoff of the ST-E2. I'm not a professional, so I could not justify the cost of pocket wizards. The Yongnuo is less than half the price of the ST-E2, has worked very well and even rotates in the hotshoe so it can be aimed better at the strobes (something the RT-E2 doesn't do). If it dies on me, I can always use the 7D's on-camera trigger, but this way I have a backup. Just something to factor in.

The effective range (about 5 meters) is very limited, plus it states that AF assist beam does not fire in wireless mode

Just out of curiosity... I am away on holidays and don't have the manuals lying around. How many meters does the ST-E2 cover, as well as the 580 EX II and 600 EX RT that I have too? I have only used the ST - E2 to control my three flashes in a studio, so I have not been concerned about the meters yet, but it is interesting.

This is so awesome. I got the 90EX bundled with the EOS M (and it wasn't advertised as such, so a true bonus), and now I can use the 600EX-RT truly off camera at last! What an awesome function to add to such a tiny flash unit.

I was also thinking about the Yongnuo st-e2, but I'm not sure if it's compatible with the 6D.

I was going to suggest this and their lights rather than screwing around with optical triggering. There is another thread here somewhere (here) discussing what it can do. The idea of firing Canon-type wireless lights with a different-brand body is intriguing.